This application claims the priority of Korean Patent Application No. 2002-25136, filed May 7, 2002, which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to the field of display devices and video sources, and more particularly, to a method for detecting an active video area for a display device and a method for mapping coordinates between a video source and a display device using the detected active video area.
2. Description of the Related Art
An independent coordinate system is used in a display device and a video source which supplies a video signal to the display device. Thus, it has been only considered that a signal is transmitted from the video source to the display device in one direction.
In conventional systems, since video data is transmitted from the video source to the display device in one direction, a user should select a region directly on the display device when the user wants to perform a predetermined function in that region of the display screen.
For example, assuming the video source is a computer and the display device is a monitor, it is well known that a screen signal is transmitted from a graphic card of a computer to the monitor in one direction. However, a function is required for mapping the predetermined area that is selected from video memory of the graphic card according to a user's demand into its counterpart area on the monitor in terms of the value corresponding to the system clock signal of the monitor. This is because when a user desires to perform a predetermined function in a predetermined region of a monitor screen, the user can readily select an area using a pointing device such as a mouse, in a corresponding position of an operating system (O/S) screen, rather than selecting an area from the monitor.
For example, when functions such as contrast and sharpness are changed only in an area on the monitor screen where a moving picture is played, the user can easily select the area from the O/S screen using the mouse and can therefore readily control related functions. It is therefore unnecessary to form an area selection terminal directly in the monitor.
FIG. 1 illustrates a relationship between a conventional coordinate system for a video source and a conventional coordinate system for a display device. Referring to FIG. 1, X and Y denote x-axis and y-axis coordinates at an arbitrary point in a video source coordinate system, respectively. In addition, X′ and Y′ denote x-axis and y-axis coordinates that are mapped in a display device coordinate system, respectively.
The relationship between the video source coordinate system and the display device coordinate system is expressed by Equation 1.
                              [                                                                      X                  ′                                                                                                      Y                  ′                                                              ]                =                                            [                                                                                                                  HE                        -                        HS                                            HMAX                                                                            0                                                                                        0                                                                                                      VE                        -                        VS                                            VMAX                                                                                  ]                        ⁡                          [                                                                    X                                                                                        Y                                                              ]                                +                      [                                                            HS                                                                              VS                                                      ]                                              (        1        )            
In order to map coordinates (X, Y) of the video source to coordinates (X′, Y′) of the display device by Equation 1, a horizontal starting point HS, a horizontal ending point HE, a vertical starting point VS, and a vertical ending point VE of the display device and a horizontal length HMAX and a vertical length VMAX of the video source coordinate system should be accurately known.
The horizontal starting point HS and the horizontal ending point HE of the display device refer to x-axis starting and ending positions, respectively, of an active video area that is measured as a horizontal clock count H_CKCNT from the starting position of a horizontal synchronous signal HSYNC in the display device coordinate system. The vertical starting point VS and the vertical ending point VE refer to y-axis starting and ending positions, respectively, of the active video area that is measured as a vertical clock count V_CKCNT from the starting position of a vertical synchronous signal VSYNC in the display device coordinate system. The active video area refers to an area of the screen in which the entire video source coordinate system is recognized in the display device coordinate system. Thus, the horizontal starting point HS, the horizontal ending point HE, the vertical starting point VS, and the vertical ending point VE are detected from a screen where a reference pattern which indicates the entire video source coordinate system is embedded, and thus, the active video area is recognized.
The horizontal synchronous signal HSYNC is a signal that is used to synchronize a horizontal line and is generated whenever a horizontal line begins. The vertical synchronous signal VSYNC is a signal that is used to synchronize a frame and is generated whenever a frame begins.
The horizontal length HMAX and the vertical length VMAX refer to an x-axis maximum length and a y-axis maximum length in the video source coordinate system, respectively. The horizontal length HMAX and the vertical length VMAX are determined depending on the screen resolution of the video source, and thus the horizontal starting point HS, the horizontal ending point HE, the vertical starting point VS, and the vertical ending point VE need to be read by the display device. For example, when the screen resolution of the computer is set to 800×600, the horizontal length HMAX and the vertical length VMAX are 800 and 600, respectively.
However, certain problems occur when four signals, i.e., the horizontal starting point HS, the horizontal ending point HE, the vertical starting point VS, and the vertical ending point VE, are detected by the display device.
When a video signal to be displayed on the display device is a continuous analog signal, the following problems occur when the active video area is detected by the display device.
FIG. 2 illustrates two examples of a waveform of a video signal. In general, a video signal appears after a predetermined amount of time passes, following generation of a horizontal synchronous signal, which indicates the start of a horizontal line.
In order to determine the existence of the video signal in a predetermined area, a black level should be clearly defined. The black level is a critical value which indicates the range under which a video signal does not exist. When the level of a signal is less than the black level, a video signal does not exist in that signal.
Thus, when a received analog video signal is compared with the black level using a comparator, if the level of the analog video signal is greater than the black level, a video signal exists. If not, the video signal does not exist.
However, when an unprocessed analog video signal is compared with the black level using the comparator to determine the existence of a video signal, the difference between the waveform of the signal and the black level is not always clear.
In part (a) of FIG. 2, the video signal is primarily comprised of signals larger than the black level. In this case, it is easy to determine the existence of the video signal. In part (b) of FIG. 2, the video signal includes signals near the level of the black level. Thus, in this case, it is difficult to determine the existence of the video signal. Hence, it is difficult to detect the active video area.
FIG. 3 illustrates the screen of the display device with a brightness gradient. As shown in FIG. 3, in the case of the screen with a brightness gradient, if the black level is varied into first, second, and third levels (Level 1, Level 2, and Level 3) according to variations in temperature or process, the area that is recognized as the video signal, i.e., the active video area, is accordingly changed into first, second, and third areas VD_OUT1, VD_OUT2, and VD_OUT3, respectively.
FIGS. 4 and 5 illustrate cases where the background screen of the display device is used to explain the difficulty in recognizing the active video area.
As shown in FIG. 4, assuming a user designates the background color of a screen as black or a color close to black and assuming objects excluding black are placed on the screen, when the user intends to obtain position information of the active video area using an unprocessed analog video signal, under the same conditions, the possibility that the active video area is incorrectly measured is increased as compared to the case where the background color is white.
Thus, as shown in FIG. 4, even though the background screen is actually in the active video area, if the background screen is black, it is recognized that the video signal exists only in icons or a status bar that are any color other than black. Thus, the position information of the active video area cannot be accurately obtained.
As shown in FIG. 5, when objects move on the black background screen, the active video area may be changed whenever the active video area is detected by the display device. Because of the emergence of multimedia functions that involve the movement of decoration icons of the screen, in the case of a dynamic background screen, as in a gray ball-shaped icon which moves on the black background screen shown in FIG. 5, the area that is recognized as the active video area varies at each movement.
Thus, a method for clearly recognizing the active video area on the display video is required in any case. The analog video area should be clearly recognized so that the coordinates of the video source are correctly mapped to the coordinates of the display device, for example according to the relationship of Equation 1.